Single channel analysis of the inward rectifier K current in the rabbit ventricular cells.

Abstract

The inward rectifier K channel in rabbit ventricular cells was studied by the patch-clamp method. Single channel currents were recorded in giga-sealed cell-attached patches with 150 mM K+ in the pipette. The slope conductance in the membrane potential range from -140 to -40 mV was 46.6 .+-. 6.7 pS [pico Siemen] (mean .+-. SD, n = 16), and was reduced by decreasing [K+] in the pipette (20 or 50 mM). The channel was blocked by an application of Cs+ or Ba2+ (0.04-1 mM) in the pipette. Outwardly directed current, recorded with 50 mM K+ in the pipette, revealed the inward rectification of the single channel current. The probability of the channel being open was 0.33 .+-. 0.05 (n = 10) at the resting potential (RP = -81.7 .+-. 1.7 mV, n = 16) with 150 mM K+ in the pipette, and it decreased with hyperpolarization. The mean open time of the channel was 178 .+-. 25 ms (n = 6) at RP. The closed time of the channel seemed to have 2 exponential components, with time constants of 11.0 .+-. 2.0 ms and 1.92 .+-. 0.52 s (n = 6) at RP. The slower time constant was increased with hyperpolarization. The averaged patch current recorded upon hyperpolarizing pulses demonstrated a time-dependent current decay as expected from the single channel kinetics. Evidently, the inward rectifier K+ current has time- and voltage-dependent kinetics.